Abstract
This paper focuses on a differential voltage measurement in low-voltage automotive devices whose subunits are separated with a low-side safety switch. In contrast to conventional applications with high-side switches, a common-mode voltage (CMV) with negative polarity exists at the input of the signal conditioning circuitry. To overcome the shortage of dedicated integrated circuits capable of withstanding negative CMV, the paper investigates single- and two-stage differential circuits with single-supplied operational amplifiers to find a cost-optimized counterpart. In addition, the proposed procedure tunes the circuit parameters in such a manner to obtain the largest possible full-scale range at the output. Though, such optimization results in very uncommon values for gain and reference voltages. This issue is additionally evaluated for reference voltages that are either cost-effective or more easily accessible to increase the circuit feasibility. Since the impact of resistances on circuits’ behaviour could be diminished to a great extent using high-precision and matched pair resistors, the sensitivity analysis was investigated only for a reference voltage change. Furthermore, a reversed termination of measured voltages results in a simplified reference voltage selection without hindering circuits’ performance, proven by simulation and experimental results.
Highlights
Ever all subunits of an electronic device in a modern vehicle share the same reference [1,2], i.e., ground potential
A set of voltage measurements was performed on a laboratory prototype of an advanced 3.7 kW DC/DC converter (Figure 15), designed for the automotive industry to validate the proposed calculation procedure
Since the safety switch separates both parts of the converter, the conditioning circuits are subjected to a negative common-mode voltage (CMV) when the switch is disconnected
Summary
Ever all subunits of an electronic device in a modern vehicle share the same reference [1,2], i.e., ground potential. A control scheme of a modern converter [7,8,9] contains numerous signal conditioning circuits [10,11], generally interfaced with a supervising microcontroller [12,13], to acquire currents and voltages and to supervise its operation This case is addressed and clarified on a simplified converter scheme (Figure 1) that consists of two subunits whose negative terminals are connected through a low-side safety switch. The magnitude of the common-mode voltage (CMV) at the input of the signal conditioning circuit may, as a result, vary extensively and can change with a high slew rate during low-side switch transitions.
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